Interaction of upgoing auroral H+ and O+ beams

Abstract

Data from the S3‐3 and DE 1 satellites are analyzed to study the interaction between H+ and O+ ions in upgoing auroral beams. Every data set analyzed showed some evidence of an interaction. The measured plasma was found to be unstable to a low‐frequency electrostatic wave that propagates at an oblique angle to . A second wave, which can propagate parallel to , is weakly damped in the plasma studied in most detail. It is likely that the upgoing ion beams generate this parallel wave at lower altitudes. The resulting wave‐particle interactions qualitatively can explain most of the features observed in ion distribution functions. H+ ions in the low‐velocity tail of the H+ beam are decelerated and O+ ions in the high‐velocity tail of the O+ beam are accelerated through this process. This may explain the occasional observation of O+ beams with substantially higher streaming energies than the simultaneously observed H+ beams. The wave‐particle interactions also can explain the asymmetrical features that regularly are seen in H+ and O+ distribution functions. The wave which was found to be unstable in the measured plasma primarily accelerates O+ perpendicular to Bo. This process can produce weakly conical O+ distributions which are characterized by T⊥ > T∥ rather than by having a peak at 90° pitch angle within the acceleration region. In general, the interaction between different ion species in multicomponent beams appears to be a dominant factor in determining the structure of upgoing auroral ions. The same process is likely to be important in a number of other beam‐containing space plasmas.